Periodic Properties of Elements in the Periodic Table

Periodic Properties of

Elements in the Periodic Table

Presented By

Dr. Lali Thomas Kotturan

Periodic Table (Modern Form)

Periodic Law

◼

The properties of elements are a

periodic function of their atomic number

P = F(z)

Periodic Law

◼

When elements are arranged in order of atomic number, similar properties recur periodically.

Li

Na

K Atomic radii vs. Z

Periodic Law

Atomic number

First Ionization Energy

Why Periodic Law?

Chemical and

Physical properties

Type of Bonding and

structure

Atomic

properties

Atomic number

Ionization Energies

H

He Ne

Ar

Li Na K

N Be

B

C O F

Mg

P

Al

Si S Cl

Ca

Atomic number

First I.E.

Variations:

1. Across a period 2. Down the group

Atomic radius

H He Li

Na

Ne Ar

K

Be

Mg

Ca

H 37

He 54 Li

156 Be 105

B 91

C 77

N 71

O 60

F 67

Ne 80 Na

186

Mg 160

Al 143

Si 117

P 111

S 104

Cl 99

Ar 96 K

231

Ca 197

Sc 161

Ti 154

V 131

Cr 125

Mn 118

Fe 125

Co 125

Ni 124

Cu 128

Zn 133

Ga 123

Ge 122

As 116

Se 115

Br 114

Kr 99 Rb

243 Sr 215

Y 180

Zr 161

Nb 147

Mo 136

Tc 135

Ru 132

Rh 132

Pd 138

Ag 144

Cd 149

In 151

Sn 140

Sb 145

Te 139

I 138

Xe 109 Cs

265 Ba 210

Hf 154

Ta 143

W 137

Re 138

Os 134

Ir 136

Pt 139

Au 144

Hg 147

Tl 189

Pb 175

Bi 155

Po 167

At 145

Rn

La 187

Ce 183

Pr 182

Nd 181

Pm 181

Sm 180

Eu 199

Gd 179

Tb 176

Dy 175

Ho 174

Er 173

Tm 173

Yb 194

Lu 172

Atomic Radius (pm) 1pm=1x10^-12m

Electronegativity

H

He Ne Ar

F

Cl

Li Na K Ca

Atomic number

Electronegativity

H 2.1 Li

1.0 Be 1.5 Na

0.9

Mg 1.2

Al 1.0 K

0.8

B

2.0 C 2.5

N 3.0

O 3.5

F 4.0 Al

1.5 Si 1.8

P

2.1 S

2.5 Cl 3.0

Ne - Ar

- He

- Increase in electronegativity

Decrease

Melting Points

m.p./^oC

1000 2000 3000 4000

0 5 10 15 20

Atomic number

-1000 0

C

Si

He Ne Ar

Ca

Melting Points

H

-259

Li

180 Be

1280

Na

97.8

Mg

650

Ca

850

K

63.7

B

2300 C

3730

N

-210

O

-218

F

-220

Al

660 Si

1410

P

44.2 S

119 Cl

-101

Ne

-249

Ar

-189

He

-270

Unit: ^oC Increase

Periodic Variation of Physical Properties

◼

Structure & Bonding

◼

Giant metallic → Giant covalent

→ Simple molecular

Periodic Variation of Chemical Properties

◼

Formulae of hydrides, oxides, chlorides

◼

Hydrolytic behaviours and

explanations

Peiodicity in formulae

Li Be B C N O F Ne Na Mg Al Si P S Cl Ar 6

4 2

Moles of Cl atoms per mole of atoms of element

Hydrides

Period 2 LiH BeH₂ B₂H₆ CH₄ NH₃ H₂O HF Period 3 NaH MgH₂ AlH₃ SiH₄ PH₃ H₂S HCl

Ionic Covalent with some ionic

character

Typically Covalent

Polar

covalent

Hydrides

Bonding Hydrolytic behaviour

Ionic NaH + H₂O → NaOH + H₂ (H^- + H₂O → OH^- + H₂)

Be(OH)₂, Mg(OH)₂, Al(OH)₃ are alkaline H₃BO₃ is acidic

Covalent with ionic character

BeH₂ + 2H₂O → Be(OH)₂ + 2H₂ MgH₂+ 2H₂O → Mg(OH)₂ + H₂ B₂H₆ + 6H₂O → 2H₃BO₃ + 6H₂ AlH₃ + 3H₂O → Al(OH)₃ + 3H₂

Hydrides

Typically Covalent

CH₄ does not dissolve nor react

SiH₄ reacts to give SiO₂.2H₂O + H₂ PH₃ very slight soluble

Si H

H H

H :OH₂ Si

H

H OH

H

+ H₂ etc

Hydrides

Polar covalent NH₃ + H₂O → NH₄⁺ + OH^- H₂S + H₂O → H₃O⁺ + HS^- HF + H₂O → H₃O⁺ + F^- HCl + H₂O → H₃O⁺ + Cl^- Note: From gp4 to gp7

Acidity increases because polarity of bond increase

Check point 38-3

H-O-H + :NH₃ OH^- + NH₄⁺ H₂O: + H-Cl H₃O⁺ + Cl^-

N is more electronegative, hence more basic than Cl.

It reacts with water by donating its lone pair electron.

CH₄ , due to its non-polar covalent bond, it does not dissolve nor react with water.

Oxides

Ionic

Ionic with

Covalent character Amphoteric Al₂O₃

Covalent Acidic CO₂

SO₂ NO₂ Basic

Na₂O

Ionic Oxides

O^2- + H₂O → 2OH^-

Na₂O(s) + H₂O(l) → 2NaOH(aq) Li₂O(s) + H₂O(l) → 2LiOH(aq) MgO(s) + H₂O(l) → Mg(OH)₂(s)

Amphoteric Oxides

Al₂O₃ + 6H⁺ → 2Al³⁺ + 3H₂O

Al₂O₃ + 2OH^- + 3H₂O → 2[Al(OH)₄]^- BeO + 2H⁺ → Be²⁺ + H₂O

BeO + 2OH^- + H₂O → [Be(OH)₄]^2-

Covalent Oxides

O=X^+ :O-H

H [O-X-OH]^- + H⁺ Mechanism of the Hydrolytic behaviour of covalent oxides:

CO₂ + H₂O  H₂CO₃  H⁺ + HCO₃^- SO₂ + H₂O  H₂SO₃  H⁺ + HSO₃^- 2NO₂ + H₂O → HNO₃ + HNO₂

Covalent Oxides

P₄O₆ and P₄O₁₀ :

P₄O₆(s) + 6H₂O(l), cold → 4H₃PO₃(aq)

P₄O₆(s) + 6H₂O(l), hot→ 3H₃PO₄(aq) + PH₃(g) P₄O₁₀(s) + 6H₂O(l) → 4H₃PO₄(aq)

The actual reactions are complicated.

The products formed depend on the amount of water present and the conditions of reaction.

Covalent Oxides

Group VIIA: F₂O, Cl₂O and Cl₂O₇

F₂O(g) + H₂O(l) → 2HF(aq) + O₂(g) Cl₂O(g) + H₂O(l) → 2HOCl(aq)

Cl₂O₇(l) + H₂O(l) → 2HClO₄(aq)

Cl

O O

O O

Cl O

O O Cl₂O₇(g)/(l)

Cl

O O

O O

Cl O

O O

+ -

Cl₂O₇(s)

Check point 38-4

a. SiO₂ does not react with water. The giant covalent structure has high lattice energy.

It is not possible to break it down in aqueous solution.

Chlorides

LiCl

NaCl MgCl₂

Ionic

AlCl₃ BeCl₂

Intermediate with covalent character

BCl₃ CCl₄ SiCl₄

NCl₃ PCl₅ PCl₃

OCl₂ S₂Cl₂ SCl₂

ClF Cl₂

Covalent

Ionic chlorides

◼

Group IA

◼ LiCl, NaCl are not hydrolysed in aqueous solution, neutral solution formed when dissolved. NaCl (s)

→ Na⁺(aq) + Cl^-(aq), LiCl (s) → Li⁺(aq) + Cl^-(aq)

◼

Group IIA

◼ MgCl₂ is not hydrolysed.

◼ Hydrated crystals undergoes hydrolysis when

heated. MgCl₂.6H₂O → MgCl(OH) + 5H₂O + HCl

Intermediate chlorides

BeCl₂ and AlCl₃ : Be²⁺ and Al³⁺

High charge/size ratio, strong polarizing power, cation hydrolysis.

Be²⁺ :O H H

:OH₂

Be(OH)₂ + HCl BeCl₂ + 2H₂O

AlCl₃ + 3H₂O → Al(OH)₃ + 3HCl

Covalent chlorides

Group IIIA BCl₃ Cl

Cl

Cl B^+ :OH₂

Due to presence of vacant orbital and the polar B-Cl bond.

BCl₃ reacts vigorously with water to give boric acid, H₃BO₃ and HCl.

BCl₃(l) + 3H₂O(l) → H₃BO₃ (aq) + 3HCl(aq)

Covalent chlorides

Group 4A : CCl₄ and SiCl₄

Cl

Cl Cl

Si Cl Cl

Cl Cl

C Cl

CCl₄ does not hydrolyzed by water SiCl₄ hydrolyzes.

SiCl₄(g) + 4H₂O(l) → SiO₂.2H₂O(s) + 4HCl(aq)

Covalent chlorides

Group VA: NCl₃

NCl₃(l) + 3H₂O(l) → NH₃(aq) + 3HOCl(aq)

chloric(I) acid

N does not have low-lying vacant orbital,

it hydrolyses through the donation of lone pair

electron of N atom to the H atom of water molecule.

:O H

H :N^-Cl₃

Covalent chlorides

Group VA: PCl₃ and PCl₅

PCl₃(l) + 3H₂O(l) → H₃PO₃(aq) + 3HCl(aq) PCl₅(s) + 4H₂O(l) → H₃PO₄(aq) + 5HCl(aq)

P is less electronegative than Cl.

PCl₃ and PCl₅ hydrolyze by accepting the electron pair from water molecule.

Covalent chlorides

Group VI: SCl₂ , S₂Cl₂

SCl₂(g) + H₂O(l) → HSCl(aq) + HOCl(aq)

S₂Cl₂(l) + 2H₂O(l) → H₂S(g) + SO₂(g) + 2HCl(aq) Group VII: FCl, Cl₂

FCl(g) + H₂O(l) → HF(aq) + HOCl(aq) Cl₂(g) + H₂O(l) → HCl(aq) + HOCl(aq)

Check point 38-5

Give the equation for the reaction between the following compounds with water:

a. AlCl₃ b. Cl₂O₆

Past paper questions

Periodicity 1999 IIA 3c 2001 IIA 3c